A fastener of the type here contemplate, described in U.S. Pat. No. 3,200,464, comprises a male and a female portion of resilient plastic material provided with respective strap-engaging means such as hooks or eyes. The female portion forms a guide channel which is bounded by a substantially rectangular frame and has a cross-member remote from its strap-engaging means, a slot of this cross-member registering with the guide channel to enable the insertion of a flat shank of the male portion into the latter. A tongue attached to the leading end of the shank extends rearward within a cutout thereof from which it resiliently projects; a free edge of that tongue is engageable with a shoulder of the cross-member in a fully inserted position of the shank, referred to hereinafter as a locking position, to prevent a spontaneous separation of the two portions from each other.
The fastener can be opened by a disengagement of the tongue from the cross-member of the frame. The tongue is accessible for this purpose from the side of the frame opposite the inserted shank; this access opening, however, is rather narrow in small fasteners of the type here primarily considered in which the shank of the male portion has a width on the order of 1 cm. The user, therefore, will generally be able to reach the even narrower tongue only with a fingernail or possibly with a pointed tool, neither of which is very convenient.